High intensity discharge lamps require a certain warm-up period, approximately five minutes, before the light output of the high intensity lamp reaches usable levels. Also, if a supply voltage drop is experienced, the high intensity lamp will extinguish and will not again reach a usable light output until after a substantial cool-down period and subsequent restart period; an accumulative period of approximately 15 minutes. In certain applications for these lamps, the period prior to attaining full luminescence after the period subsequent to a supply voltage drop in which the lamp is extinguished can result in substantial inconveniences. In certain specific applications such as hospitals, supermarkets, and department stores, sudden light failure resulting from a voltage drop can cause patients or patrons to expose themselves or others to injury.
Accordingly, control devices for auxiliary lamps have been sought to automatically provide auxiliary lighting when the high intensity discharge lamp is in a low luminescence condition. However, control devices have not been readily available for an auxiliary light source for use with electronic high intensity discharge lamp ballasts to provide supplemental lighting during start-up and cool-down phases of operation of an associated high intensity discharge lamp.
The provision of an auxiliary control circuit for an auxiliary lamp which automatically functions to provide lighting during times when the high intensity discharge lamp is not at full luminescence can encounter an operational frequency mismatch of the 50/60 Hz frequency operation of conventional power supplies and the 100 Hz-400 kHz frequency of operation of high intensity discharge lamp ballasts. Additionally, conventional auxiliary lamps may use a power source of 120 Vac whereas high intensity discharge lamp electronic ballasts operate over a range of voltages of from 120-277 Vac.
Electronic HID ballast systems for HID lamps have been provided as alternatives to traditional magnetic ballasts in both low wattage applications and mid-wattage applications of 50 to 450 watts, although low wattage HID lamps frequently have not used auxiliary emergency lighting sources. Auxiliary quartz lamp lighting systems now are used for mid-wattage (50-450 watts) HID lamps with electronic ballasts.